In order to use Nuclease-T' as a testing object for the relationship between the Global potential function (operating in the ordered structure of proteins and binding the polypeptide chain) and the local potential functions (controlling local interactions between residues), the X-ray diffraction patterns of crystalline Nuclease-T' have been investigated at 17 planes through the reciprocal lattice and the data from approximately 7000 reflections is being treated. In an attempt to crystallize semisynthetic Nuclease-T', Nuclease-T-(6-48) has been synthesized and purified to essentially homogeneity as judged by a two-dimensional peptide map of a tryptic digest. The idea that the global potential function is not operative in fragments has been tested. The dissociation constant of deoxythymidine-3', 5'-diphosphate (pdTp) with Nuclease-(1-126) in the presence of 10 to the minus 2nd power M Ca ion was found to be approximately 5 times 10 to the minus 5th power M. Then, it was observed that Nuclease-(1-126) bound with pdTp exhibits a Stokes radius slightly greater than that of nuclease A, no resistance against tyrpsin digestion and a greater intrinsic viscosity than that of nuclease A (the report of the previous year). Thus, the polypeptide chain of Nuclease-(1-126) is not bound even in the liganded form.